Police said the accident occurred on an arterial road late at night; the girl lost balance mid-ride and the trailing car could not avoid her.

After confirming the rider fled without rendering aid, Tokyo police launched a hit-and-run manhunt for breach of the duty to rescue.

Japan has seen a string of two-wheeler passenger accidents, prompting tougher helmet enforcement and late-night street-racing crackdowns.

Experts repeated calls for protective gear for pillion passengers and restraint from hard acceleration.

Late-night motorcycle accidents and rescue-duty questions recur in Korea and Taiwan as well, drawing interest in how penalties compare.